The present invention relates to a composition for slush molding, more particularly to a slush molding composition capable of producing molded articles suitable for automotive trims such as instrument panels.
Slush molding process has been widely practiced for molding various articles as interior component parts of motor vehicles. In this molding, there have been proposed modifications of PVC with flexible thermoplastic polyurethane resin as materials to provide soft touch without a low molecular weight plasticizer, as disclosed in Examined Japanese Patent Publication Nos. S53-29705, S59-39464 and S60-30688.
It is an object of the present invention to provide a molded article of improved compatibility of plasticizer and soft feel even at low temperature. It is another object of the present invention to provide a molded article of little or reduced fogging problem (formation of oil film of evaporated plasticizer on the automotive front windshield) and suitable for automotive instrument panels. It is a further object of the present invention to provide a molded article having improved pigment dispersibility without causing uneven color even in light color. It is still another object of the present invention to provide a molded article having improved durability such as resistance to chemicals. It is yet another object of the present invention to provide a slush molding composition and a process, capable of producing a molded article as above.
Briefly, these and other objects of this invention as hereinafter will become more readily apparent have been attained broadly by a slush molding composition, comprising a thermoplastic polyurethane elastomer (A) mainly comprised of a diol component including an aromatic ring-containing diol and a non-aromatic diisocyanate, and a plasticizer (B). The thermoplastic polyurethane elastomer (A) usually has a number average molecular weight (measured by GPC, hereinafter referred to as Mn) of about 10,000 to about 50,000.
Suitable thermoplastic urethane elastomers (A) according to the present invention include, for example, those desclosed in U.S. Pat. No. 5,906,704, herein incorporated by reference. Illustrative of (A) are ones obtainable by reacting an NCO-terminated urethane prepolymer (a) with a non-aromatic diamine (b1) and an aliphatic monoamine (b2). Said prepolymer (a) is derived from an excess non-aromatic diisocyanate (a1) and a high-molecular diol (a2) having a number average molecular weight of 500 to 10,000 with, optionally, a low-molecular diol (a3). At least a part of the diol component comprising (a2) and optionally (a3) should be aromatic ring-containing diols so as to attain the durability required as slush molding composition.
Suitable non-aromatic diisocyanates (al) include, for example, {circle around (1)} aliphatic diisocyanates with 2 to 18 carbon atoms (except the carbon atoms in the NCO groups, similarly hereinafter), e.g., ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (hereinafter referred to as HDI), dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethyl caproate, bis(2-isocyanatoethyl)fumarate, bis (2-isocyanato ethyl) carbonate, 2-isocyanatoethyl-2,6-diisocyanatohexanoate, and the like; {circle around (2)} alicyclic diisocyanates with 4 to 15 carbon atoms, e.g., isophorone diisocyanate (hereinafter referred to as IPDI), dicyclohexylmethane-4,4xe2x80x2-diisocyanate (hereinafter referred to as hydrogenated MDI), cyclohexylene diisocyanate, methyl cyclohexylene diisocyanate (hereinafter referred to as hydrogenated TDI), bis(2-isocyanato ethyl)-4-cyclohexene, and the like; {circle around (3)} araliphatic isocyanate with 8 to 15 carbon atoms, e.g., m- and/or p-xylylene diisocyanate (hereinafter referred to as XDI), xcex1, xcex1, xcex1xe2x80x2, xcex1xe2x80x2-tetramethyl xylylene diisocyanate (hereinafter referred to as TMXDI), and the like; {circle around (4)} modified diisocyanates from these, e.g., diisocyanates having a carbodiimide group, an urethodione group, an urethoimine group or an urea group; and {circle around (5)} mixtures of two or more of those compounds.
Among these compounds, preferred are alicyclic diisocyanates, particularly IPDI and hydrogenated MDI.
Suitable high molecular weight diols (a2) include polyester diols, polyether diols and mixtures of two or more of those compounds.
As the aforesaid polyester diol can be cited: {circle around (1)} polycondensates between a dihydric alcohol and a dicarboxylic acid or its ester-forming derivative (acid anhydride, lower alkyl ester with one to 4 carbon atoms, acid halide, and the like); {circle around (2)} ring opening polymerizates of a lactone monomer with a dihydric alcohol as initiator; and mixtures of two or more of those compounds.
Suitable dihydric alcohols include low molecular weight diols and polyether diols. Examples of low molecular weight diols include: aliphatic dihydric alcohols [linear diols such as ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, and the like, branched diols such as propylene glycol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, and 2,3-butanediol]; alicyclic dihydric alcohols [1,4-bis(hydroxymethyl)cyclohexane diol, 2,2-bis(4-hydroxycyclohexyl)propane and the like]; aromatic ring-containing dihydric alcohols [m-xylylene glycol, p-xylylene glycol, alkylene oxide adduct (molecular weight: less than 500) of bisphenols such as bisphenol A, bisphenol S or bisphenol F. alkylene oxide adduct (molecular weight: less than 500) of dihydroxynaphthalene and bis(2-hydroxyethyl)terephthalate]. Suitable polyether diols include the same ones as described below. Mixtures of two or more of these diols may also be used.
Of these compounds preferable are aromatic ring-containing dihydric alcohols(particularly alkylene oxide adducts of bisphenol A), and combinations thereof with aliphatic dihydric alcohols or alicyclic dihydric alcohols.
Examples of the dicarboxylic acid or its ester-forming derivative in aforesaid {circle around (1)} include: aliphatic dicarboxylic acids with 4 to 15 carbon atoms such as succinic, adipic, sebacic, glutaric, azelaic, maleic and fumaric acids; aromatic dicarboxylic acids with 8 to 12 carbon atoms such as terephthalic and isophthalic acids; their ester-forming derivatives such as acid anhydrides, lower alkyl esters (e.g., dimethyl ester, diethyl ester), acid halides (e.g., acid chloride); and mixtures of two or more of these compounds. It is preferable to use aromatic dicarboxylic acids of these compounds in order to introduce an aromatic-ring into (A).
Examples of the lactone monomer in aforesaid {circle around (2)} include xcex3-butyrolactone, xcex5-caprolactone, xcex3-valerolactone and mixtures of two or more of these compounds.
As the aforesaid polyether diol can be cited alkylene oxide adducts of dihydric phenols.
Among the dihydric phenols are bisphenols, e.g., bisphenol A bisphenol F and bisphenol S, and monocyclic phenols e.g., catechol and hydroquinone.
Suitable alkylene oxides include ones containing 2-8 carbon atoms, for example, ethylene oxide (hereafter, referred to as xe2x80x9cEOxe2x80x9d), propylene oxide (hereafter, referred to as xe2x80x9cPOxe2x80x9d), 1,2-butylene oxide, 1,3-butylene oxide, 1,4-butylene oxide, 2,3-butylene oxide, styrene oxide, xcex1-olefin oxide with 5 to 10 or more carbon atoms, epichlorohydrin, and combinations of two or more of these compounds, which may be added blockwise and/or randomwise.
Of those polyether diols, preferable are oxyalkylated dihydric phenols, and particularly oxyethylated bisphenols.
Of those high molecular weight diols (a2), preferable are polyester diols, more preferable condensed polyester diols derived from at least one aromatic ring-containing dihydric alcohol and at least one aromatic dicarboxylic acid, particularly preferable a condensed polyester diol derived from an alkylene oxide (particularly EO and/or PO) adduct of bisphenol A and iso- and/or terephthalic acid.
(a2) generally has an Mn of 500 to 10,000, preferably 800 to 5,000, more preferably 1,000 to 3,000. Soft touch is not obtained in case the number average molecular weight is lower than 500, while the required strength is not attained when it is higher than 10,000.
Mn used herein can be calculated on the basis of a calibration curve obtained from a molecular weight standard sample such as polystyrene using gel permeation chromatography (GPC).
As the low molecular weight diol (a3) in combination with (a2) as necessary, the compounds cited as starting materials for the aforesaid polyester diols can be used. Preferable as (a3) are aliphatic diols and oxyalkylated bisphenols, particularly oxyalkylated bisphenol A.
The molar ratio of the respective constituent parts making up the NCO-terminated urethane prepolymer (a) before producing the elastomer (A) to 1 mole of (a1) is this: (a2) generally 0.1 to 0.5 mole, and preferably 0.2 to 0.4 mole; (a3) generally 0 to 0.2 mole, and preferably 0.05 to 0.15 mole.
Equivalent ratio of NCO/OH is usually 1.5-2, particularly 1.7-1.9.
The content of free isocyanate group in the urethane prepolymer (a) is generally one to 10 wt %, preferably 3 to 6 wt %.
Suitable non-aromatic diamines (b1) include, for example, cycloaliphatic diamines containing 4-15 carbon atoms, such as 4,4xe2x80x2-diamino-3,3xe2x80x2-dimethyldicyclohexylmethane, 1,4-diaminocyclohexane, isophoronediamine; aliphatic diamines containing 2-18 carbon atoms, such as ethylenediamine, hexamethylenediamine; araliphatic diamines containing 8-15 carbon atoms, such as xylylenediamine, xcex1, xcex1, xcex1xe2x80x2, xcex1xe2x80x2-tetramethylxylylenediamine; and mixtures of two or more of these compounds. Among these compounds preferred are cycloaliphatic diamines and aliphatic diamines, particularly isophoronediamine (hereinafter referred to as IPDA) and hexamethylenediamine.
Suitable monoamine (b2) include monoalkylamines and dialkylamines, containing 1-8 carbon atoms in the alkyl group, such as methylamine, ethylamine, n- and i-propylamines, n- and i-butylamines, dimethylamine, diethylamine, di-n- and -i-propylamines, di-n- and i-butylamines and the like; mono- and di-alkanolamines, containing 2-4 carbon atoms in the hydroxyalkyl group, such as monoethanolamine, diethanolamine and the like; and mixtures of two or more of these compounds. Among these compounds, preferred are dialkylamines, particularly di-n-propylamine and di-n-butylamine.
Molar ratio of (b1)/(b2) is generally 20/1-5/1, particularly 15/1-8/1.
In the above reaction for formation of (A), an equivalent ratio of the amino group of (b1) to the isocyanate group of (a) is usually from 0.2 to 0.7, and preferably from 0.3 to 0.6, while an equivalent ratio of the amino group of (b2) to the isocyanate group of (a) is usually from 0.02 to 0.2, and preferably from 0.05 to 0.15.
Preparation methods and conditions of (a) and (A) include those disclosed in U.S. Pat. No. 5,906,704., herein incorporated by reference.
In practice of the present invention, the thermoplastic polyurethane elastomer (A) is used in powder-form. Suitable methods for producing powder of (A) are not specifically limited but include, for example, the following methods:
{circle around (1)} method of grinding blocked or pelletized (A) through techniques, such as freeze-grinding or icing-grinding;
{circle around (2)} method of forming a non-aqueous dispersion of (A) in an organic solvent which does not dissolve (A) (e.g. n-hexane, cyclohexane, n-heptane, etc.) and separating (A) from the non-aqueous dispersion with drying (e.g. method described in Unexamined Japanese Patent Publication No. H04-255755, etc.); and
{circle around (3)} method of preparing a water dispersion of (A) in water containing a dispersant and separating (A) from the water dispersion with drying (e.g. methods described in Unexamined Japanese Patent Publication Nos. H07-133423 and H08-120041).
Among them, the method of {circle around (3)} is preferred in that a powder having a desired particle size can be obtained without using a large amount of the organic solvent.
Mn of (A) is generally 10,000 to 50,000, and preferably 15,000 to 30,000. If Mn is less than 10,000, no molded article having the required breaking strength can be obtained. But Mn higher than 50,000 would increase the hot-melt viscosity, affecting the moldability.
The content of aromatic-ring in said (A) is generally from 5 to 50 wt % on the total weight of (A), and preferably from 10 to 40 wt %. When the content is less than 5 wt %, the molded aiticle can have no satisfactory durability. The content exceeding 50 wt % would increase the hot-melt viscosity, affecting the moldability.
The heat-softening initiation temperature (hereinafter referred to as HIT) of (A) is generally from 120 to 200xc2x0 C., and preferably from 130 to 150xc2x0 C. When the HIT is lower than 120xc2x0 C., the blocking between particles of the resin is liable to occur. On the other hand, when the HIT is higher than 200xc2x0 C., it becomes sometimes difficult to obtain a molded article having a smooth surface.
The term xe2x80x9cHITxe2x80x9d used in the present specification can be measured in accordance with the method (TMA) described in JIS K-7196 (1991).
Suitable plasticizers (B) include those mentioned as examples of solbilizer in U.S. Pat. No. 3,489,723, herein incorporated by reference. Exemplary of (B) are aromatic monocarboxylic acid diesters of polyalkylene glycol; phthalic acid esters, e.g., dibutyl phthalate, dioctyl phthalate, butyl benzyl phthalate, di-isodecyl phthalate; aliphatic dibasic acid esters, e.g., di-2-ethyl hexyl adipate, 2-ethyl hexyl sebacate; trimellitate esters, e.g., tri-2-ethyl hexyl trimellitate, tri-ocytl trimellitate ; fatty acid esters, e.g., butyl oleate; aliphatic phosphates, e.g., trimethyl phosphate, triethyl phosphate, tributyl phosphate, tri-2-ethyl hexyl phosphate, tributoxy phosphate; aromatic phosphates, e.g., triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, xylenyl diphenyl phosphate, 2-ethyl hexyl diphenyl phosphate, tris(2,6-dimethyl phenyl)phosphate; halogenated aliphatic phosphates, e.g., tris(chloroethyl)phosphate, tris(f-chloropropyl)phosphate, tris(dichloropropyl)phosphate, tris(tribromoneopentyl)phosphate. Those compounds are used alone or as a mixture of two or more thereof.
Among these compounds mentioned as example of said plasticizer (B), preferred are such aromatic monocarboxylic acid esters of polyalkylene glycol (Bi) as ones expressed by the following general formula (1).
R1COOxe2x80x94[Axe2x80x94Oxe2x80x94]nxe2x80x94COR2xe2x80x83xe2x80x83(1) 
In the formula, R1 and R2 represent the same or different aromatic monocarboxylic acid residues from each other, A represents an alkylene group with two to four carbon atoms, and n is an integer of two to 25.
Said residues R1 and R2 can be independently selected from phenyl group and alkyl- and/or halo-substituted phenyl group. Examples of R1 and R2 include phenyl group; and aromatic hydrocarbon groups nuclear-substituted (substitution degree: 1 to 3) with one or more alkyl groups having 1 to 10 carbon atoms and/or halogens (e.g. Cl, Br, etc.), such as toluyl, xylyl, 4-butylphenyl, 2,4-dibutylphenyl, 2-methyl-4-chlorophenyl, and nonylphenyl groups, etc.
Examples of suitable A include straight-chain or branched alkylene groups having 2 to 4 carbon atoms (e.g. ethylene group, 1,2- and 1,3-propylene group, 1,2-, 1,3-, 2,3- and 1,4-butylene groups, etc.) and alkylene groups substituted with a halogen (e.g. 1-chloromethylethylene group, 1-bromomethylethylene group, etc.).
Among them, preferred examples are those wherein R1 and 10 R2 each independently represents a phenyl group or an C1-10 alkylphenyl group and A represents an alkylene group (particularly ethylene group).
In the above general formula (1), n is usually from 2 to 25, preferably from 3 to 15, and more preferably from 3 to 10. When n exceeds 25, the solidification point exceeds 0xc2x0 C. and, therefore, soft feel of the resulting slush molded article at low temperature is lowered. On the other hand, when n is less than 2, the boiling point is smaller than 200xc2x0 C. and, therefore, fogging tends to occur.
Among said (B1), especially preferred are the compounds expressed by the following general formulas (2) and (3).
PhCOOxe2x80x94[CH2CH2xe2x80x94Oxe2x80x94]3xcx9c10xe2x80x94COPhxe2x80x83xe2x80x83(2) 
PhCOOxe2x80x94[PPG]3xcx9c10xe2x80x94COPhxe2x80x83xe2x80x83(3) 
xe2x80x9cPhxe2x80x9d in the formulas (2) and (3) represents phenyl group, and [PPG] represents the residue of polypropylene glycol containing 3-10 oxypropylene units. The most preferred is dibenzoate of polyethylene glycol having Mn of about 200 (hereinafter referred to as PEG200 dibenzoate).
The method of producing the above aromatic carboxylic acid diester (B1) is not specifically limited but includes, for example, (1) method of heating an aromatic monocarboxylic acid or its lower C1-4 alkyl ester and a polyalkylene glycol under reduced pressure and removing the produced water or alcohol and (2) method of reacting an anhydride of an aromatic monocarboxylic acid with a polyalkylene glycol, neutralizing excess monocarboxylic acid and removing it by extraction.
(B1) is used alone or in combination with other one or more plasticizers. When using in combination, the amount of (B1) contained in (B) is not less than 50% by weight, and preferably not less than 70% by weight, because good low-temperature physical properties and fogging resistance of the slush molded article are obtained.
In the slush molding composition of the present invention, the quantity to be added to the polyurethane elastomer (A) of the plasticizer (B) per 100 parts, by weight, of (A) is generally 2 to 80 parts by weight, and preferably 5 to 50 parts by weight.
If (B) is less than 2 part by weight, the melt viscosity in molding will rise, resulting faulty molding. If the addition exceeds 80 parts by weight, on the other hand, (B) will bleed out on the molded skin surface in a change with passage of time.
As the additive suitable in the present invention can be cited pigment, stabilizer and other additives.
The pigments are not particularly restricted, and known organic pigments and/or inorganic pigments can be used. The content of pigments is generally 0.01 to 5 parts by weight per 100 parts by weight of (A).
Among the suitable organic pigments are, for example, insoluble azo pigments, soluble azo pigments, copper phthalocyanine pigments and quinacridone pigments. The inorganic pigments include, for example, chromates, ferrocyanide compounds, metal oxides, sulfide selenium compounds, metallic salts (e.g., sulfate, silicate, carbonate, phosphate), metallic powder and carbon black.
The stabilizers are not particularly restricted, and known antioxidants and/or ultraviolet absorbents can be used. The content of stabilizers is generally 5 parts by weight or less per 100 parts by weight of (A).
Among the suitable antioxidants are hindered phenols such as 2,6-di-t-butyl-p-cresol and butylhydroxyl anisole; bisphenols such as 2,2xe2x80x2-methylenebis(4-methyl-6-t-butylphenol); and phosphorus compounds such as triphenyl phosphite and diphenyl isodecyl phosphite.
Among the ultraviolet absorbents are benzophenones such as 2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone; benzotriazoles such as 2-(2xe2x80x2-hydroxy-5xe2x80x2-methylphenyl)benzotriazole; salicylates such as phenyl salicylate; and hindered amines such as bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate.
The other additives contained, as necessary, in the slush molding composition of the present invention include blocking inhibitor, releasing agent, thermal resistant stabilizer, flame retarder and the like.
The following methods of preparing the slush molding composition of the present invention are given by way of example, but not limited thereto by any means.
{circle around (1)}: A powder of (A), (B) and the additives are blended in a lump in a mixer.
{circle around (2:)}: (B) and the additives are first blended, and then mixed with a powder (A).
{circle around (3)}: At an optional stage during the production of the powder of (A), (B) and part or all of additives are previously contained.
Of those methods, preferable is the method {circle around (2)} in that the preparing process is simplified.
Powder mixing apparatuses which are used in preparing the slush molding composition of the present invention are not restricted in particular, and known mixers can be used. Among suitable powder mixing apparatuses are high-speed shear ones, for example, fluid mixers such as a Henschel mixer (trade name), and low-speed ones such as a Nauta mixer and a planetary mixer. Preferred is a Henschel mixer.
The slush molding composition of the present invention is applied in the form of powder. The powder has an average particle diameter of generally 50 to 400 xcexcm, preferably 100 to 300 xcexcm, more preferably 130 to 200 xcexcm. If powder has an average particle diameter less than 50 xcexcm, then flowability of the powder will be poor, with the powder failing to be introduced into narrow parts of the mold, resulting in faulty molding. With powder having a diameter larger than 400 xcexcm, on the other hand, pin holes can be caused on the molded surface skin.
Another point is that fine particles with a particle diameter of less than 100 xcexcm is contained in the powder in an amount generally not more than 50 percent by weight, and preferably not more than 30 percent by weight. If the percentage of the particles less than 100 xcexcm in particle diameter exceeds 50 percent by weight, dusting will be caused and the powder will not flow well into the narrow areas in the mold, resulting in faulty molding.
The repose angle of the powder is usually not more than 35xc2x0, and preferably not more than 33xc2x0, while the spatula angle is usually not more than 50xc2x0, and preferably not more than 40xc2x0. When the repose angle and spatula angle are not within the above range, the flowability of the powder becomes inferior and it becomes sometimes difficult to mold because the narrow portions of the mold are not filled with powder on slush molding.
The average particle diameter mentioned here is defined as a value of 50% pass particle diameter expressed in the sieve opening through which 50 percent by weight of the sample passes as measured by particle size distribution meter, e.g., TUBUTEC manufactured by LASENTEC LTD. The repose angle and spatula angle are defined as values measured by powder tester manufactured by HOSOKAWA MICRON LTD.
Molded article made of the slush molding composition of the present invention is very useful as automobile interior material, for example, for instrument panel and also applicable to other molded articles such as sofa surface skin and other interior furniture.
Now the present invention will be described in more detail by the following examples but is by no means restricted thereto. In the following description, it is understood, part or parts mean part or parts by weight and percent denotes percent by weight. The raw materials used are supplied by the following manufacturers under the following brand-name.
[Raw material//Brand-name//Manufacturer]
EO (2 mol) adduct of bisphenol A//Newpole BPE-20T//SANYO CHEMICAL INDUSTRIES, LTD.
Polyethylene adipate diol//SANESTOR 2620//SANYO CHEMICAL INDUSTRIES, LTD.
Polyvinyl alcohol//PVA-235//KURARAY CO.,LTD.
Blocking inhibitor (finely powdered silica)//SILYSIA 978//FUJI SILYSIA CHEMICAL INDUSTRIES, LTD.
Light stabilizer//DIC-TBS//DAINIPPON INK AND CHEMICALS, INC.
Titanium oxide//TIPAQUE R-820//ISHIHARA SANGYO KAISHA, LTD.